Catheters are commonly used to perform medical procedures within very small spaces in a patient's body, and most procedures mandate precise catheter navigation. A catheter used to perform many ablation and mapping procedures generally includes a handle and a flexible elongate body (or shaft) having a distal end. Steering the distal end of a catheter can be difficult, especially as the elongate body passes through a tortuous vascular path.
Catheter tip steering is often accomplished with the use of one or more pull wires attached to a pull ring within the distal end of the catheter shaft at one end, and coupled to a steering control mechanism housed within the handle at the other end. Manipulation of the steering control mechanism will deflect the catheter tip through pulling or releasing pull force pressure on the one or more pull wires. The pull force exerted on a pull wire within a standard-sized catheter is often quite large, for example, in excess of ten pounds, and the pull force required is increased for thicker or longer catheters. Therefore, the point of connection between a pull wire and the pull ring must be able to withstand this force in order to preserve the integrity of the steering system.
Currently, the most frequently used type of joining method between a pull wire and pull ring is welding the distal end of a flat pull wire to an outer surface of a pull ring. However, this joining method is very susceptible to stress fractures and peeling as a pull force is exerted repeatedly over time (referred to herein as “destructive pull force” to distinguish from the pull force necessary to steer the catheter tip). Sometimes a round pull wire may be used that has a flattened distal end for attachment to the pull ring, but this does not provide a significant benefit over using a flat pull wire. The point in the pull wire at which the flat distal end transitions into the rounded wire body becomes another stress point when the catheter tip is repeatedly deflected. As a result, the pull wire may become detached from the pull ring, or may break at the stress point. Further, it is not uncommon for pull rings to become detached from the inside of the catheter shaft and creep away from the distal end of the catheter as a result of repeated deflections and manipulations.
A system and method of anchoring a pull wire to a pull ring in a catheter deflection mechanism is provided herein. Further provided is a system and method to enhance the strength of the join between a pull wire and pull ring so that the mechanism may reach higher levels of pull force while maintaining design integrity. For example, the system and method include an increased amount of weld sites for attaching a pull wire to a pull ring.